Waveguide structure

ABSTRACT

A waveguide structure is described wherein a section of waveguide is effectively shorted at one end thereof by a pair of conductive plates. Each of the plates is adjacent to a narrow wall of the waveguide section and extends from broad wall to broad wall across the aperture of the waveguide. The edge of one of the plates remote from the edge adjacent to a narrow wall is closely spaced from the remote edge of the other plate to form a gap between the edges midway between the narrow walls. The thickness of the plates and the spacing of the gap between the plates is arranged so that no appreciable radiation occurs due to the gap at the reflective end.

Matted States Patent Napoli [451 Apr. 4, 1 .972

[54] WAVEGUIDE STRUCTURE [21] Appl No.: 87,211

2,829,348 4/1958 Kostriza et a1. ..333/84 X 3,508,175 4/1970 Alford ..333/98 X 3,539,951 11/1970 Tischer ..333/98 X Primary ExaminerHerman Karl Saalbach Assistant Examiner-Marvin Nussbaum AttorneyEdward J. Norton 57] ABSTRACT A waveguide structure is described wherein a section of waveguide is effectively shorted at one end thereof by a pair of conductive plates. Each of the plates is adjacent to a narrow wall of the waveguide section and extends from broad wall to broad wall across the aperture of the waveguide. The edge of one of the plates remote from the edge adjacent to a narrow wall is closely spaced from the remote edge of the other plate to form a gap between the edges midway between the narrow walls. The thickness of the plates and the spacing of the gap between the plates is arranged so that no appreciable radiation occurs due to the gap at the reflective end.

6 Claims, 2 Drawing Figures WAVEGUIDE STRUCTURE This invention herein described was made in the course of or under the contract or subcontract thereunder with the Department of the Army.

The present invention relates generally to waveguides and more particularly to an end terminated waveguide structure.

Recent developments in printed circuit techniques include the introduction of strip type transmission lines which comprise a flat narrow conductor etched to or otherwise suitably fixed to printed circuit boards. These transmission lines, sometimes known as microstrip lines, are particularly advantageous to use because of their light weight and the small space they occupy. These strip transmission lines, called microstrip lines, are limited in their power handling capabilities whereas conventional waveguides are not so limited. To take advantage of the meritorious effects of each, the waveguides may be located at the high power points and the microstrip transmission lines at the low power points. This requires a transition structure to allow the very complex, low power circuits to be coupled to the high power circuits and equipment.

Heretofore, a common way of providing a transition from conventional rectangular waveguide to a microstrip transmission line was to protrude the narrow strip-like conductor and the substrate into the waveguide by means of a hole cut in the broad wall of the waveguide. The hole in the waveguide was located a quarter wavelength away from a short circuited end of the waveguide, with the narrow conductor extending therethrough in the E or electric field plane of the waveguide. Such a waveguide to strip transmission line transition structure requires precise alignment of the protruding conductor with respect to the waveguide. This alignment becomes difficult because of the lack of viewing area in the waveguide. When the circuit itself is very thin, such as on the order of 4 mils at 60 GH (gigaHertz), a slight misalignment of the waveguide with respect to the microstrip line when assembling the structure could cause fracturing of the microstrip.

Also at millimeter wavelength frequencies where the insulatin g substrate material is Gallium Arsenide, for example, the entire monolithic circuit is extremely small. The assembly and alignment of such a circuit in a waveguide becomes very critical and a better viewing is required in order to provide such alignment.

Also, with the advent of new transferred electron devices and avalanche diode devices having high efficiencies which efficiencies are dependent on the precise placement of the devices of the waveguide, it is desirable to provide a waveguide structure in which precise placement and alignment of these devices in the waveguide structure can more easily be provided.

It is an object of the present invention therefore to provide an improved close-ended waveguide structure having an aperture at the closed end for the placement and adjustment therein of transmission line circuits and devices.

Briefly this and other objects of the present invention are provided by a longitudinally extending waveguide section which is terminated at one end by a reflecting member having an elongated aperture and a pair of reflecting surfaces border-' ing opposite elongated sides of the aperture. The aperture is located so that an extension of the center line of the waveguide passes through the aperture. The width of the aperture and the longitudinal length of the reflecting surfaces bordering the aperture is determined so that upon the application of electromagnetic waves to the waveguide the reflecting member including the aperture presents an effective short circuited termination and no appreciable radiation exits through the aperture.

This invention will be better understood by reference to the following description taken with the following drawings wherein:

P16. 1 is a perspective view showing an embodiment of the present invention, and

FIG. 2 is a top plan view ofthe embodiment of FIG. 1.

Referring to FIGS. 1 and 2, a section of rectangular waveguide 10 extends through an aperture 12 in a broad ground planar conductor 11. The waveguide 10 is electrically and physically connected to the ground planar conductor 11. The waveguide 10 is made up of broad walls 13 and 15 spaced by narrow walls 17 and 19 to define an aperture 18.

The waveguide 10 is tenninated at one end by a pair of short circuiting conductive plates 21 and 22. The plate 21 is placed so that one end is adjacent to narrow wall 19 and the opposite end extends toward a center line of the waveguide 10. The plate 21 extends across the aperture from broad wall 13 to broad wall 15. The plate 22 is placed so that one end is adjacent to narrow wall 17 and the opposite end extends toward the plate 21 leaving an aperture or gap therebetween midway between the narrow walls 17 and 19. The plate 22 extends across the aperture from broad wall 13 to broad wall 15 leaving at one end of the waveguide 10 only the aperture or gap provided by the spacing between the two plates 21 and 22.

The plates 21 and 22 are located one-quarter wavelength M4) from the ground conductor 11. The broad walls 13 and 15 have a slot therein extending along the lengthwise axis of the waveguide midway between the narrow walls 17 and 19. The slots 23 and 24 extend from the gap provided by the closely spaced conductive plates 21 and 22 to the ground planar conductor 11 to form a continuous opening into the waveguide that extends into the waveguide one-quarter wavelength from the terminated end. The spacing s between the conductive plates 21 and 22 and the width of slots 23 and 24 are equal and are made sufficiently wide so as to accommodate a dielectric substrate 27 and a narrow strip-like conductor 25 on the substrate 27.

The strip-like conductor 25 is spaced from ground planar conductor 11. The narrow strip-like conductor 25, the substrate 27 and the ground planar conductor 11 form a microstrip transmission line 26. The narrow strip-like conductor 25 and substrate 27 alone extend into the aperture 18 in the E or electric field plane of the waveguide 10 so as to be in the coupling region of the waveguide one-quarter wavelength from the plates 21 and 22. The substrate 27 with the narrow strip-like conductor 25 is supported by the ground planar conductor 11 except in the apertured region. Because of the excellent viewing and access from the end of the waveguide when mounting the narrow strip-like conductor and substrate 27 on the ground conductor 11, this circuit can be easily aligned, assembled and disassembled without the problem of mis-alignment or breaking the fragile substrate.

The conductive plates 21 and 22 provide an effective short circuit by arranging the thickness t" of the plates 21 and 22 and the spacing s between the plates 21 and 22 so that no appreciable radiation exits from the aperture at the reflected end. The attenuation coefficient [a] is equal to of the parallel If it is desired, for example, that the power at the outside surface of the plates be 30 db. down or lose l/l000th of power, the following relationship is given:

Solving this relationship in terms of s and I, we get:

when 5 M2, 01

Therefore. in order for the power to be 30 db. down when the spacing s is much less than one-half wavelength, the thickness t of the plates must be approximately equal to the spacing s.

As the spacing 5 gets closer to one-half wavelength at the highest operating frequency, for example, 3 is %A at the highest operating frequency, the attenuation coefficient is reduced one-half. Even though this attenuation is reduced by one-half and t and s are approximately equal, the lost power is only about 0.15 db. By centering the slots 23 and 24 between the narrow walls little or no radiation occurs out of the waveguide when the waveguide is propagating in the dominant even mode.

In the arrangement described above, for operation at a highest frequency of 12 GH, (gigaHertz) the waveguide width W was 0.9 inch the height h was 0.45 inch, the spacing s was inch and the thickness 1 was inch. The slot width was /5 inch. The lost power was about 0.15 db. down.

in the operation of the system described above, signals propagating along the waveguide in the TE mode from terminal 31 are reflected at the short circuited end provided by plates 21 and 22. The coupling probe made up of the narrow conductor 25 on the substrate 27 couples the signal and the signal travels along the microstrip line 26 made up of narrow conductor 25, spaced by a substrate 27 from ground planar conductor 11 toward the broken cross-sectioned, terminating end 33 of microstrip line 26.

The voltage and consequently power decay through the aperture from the inner surface of the waveguide to the outer surface of the waveguide is dependent upon the thickness of the plates 21 and 22. The same power decay accomplished by the thickness of the plates can be accomplished by a pair of flanges located on either elongated side of the aperture and extending from the plates 21 and 22 in a longitudinal direction to present, as does the thickness dimension of the plates present, a pair of reflecting surfaces on either elongated side of the aperture between the plates.

What is claimed is:

l. A waveguide structure comprising:

a waveguide section having longitudinally extending conductive walls defining a waveguiding aperture adapted for the propagation of electromagnetic waves therealong over a given range of frequencies in a longitudinal direction,

a reflecting member located at one terminating end of said waveguide section, said reflecting member having an elongated aperture and a pair of reflecting surfaces bordering opposite elongated sides of said elongated aperture, said elongated aperture being located so that an extension of the center line of said waveguide section passes through said elongated aperture and between said reflecting surfaces,

the width of said elongated aperture and the length of said reflecting surfaces along the said longitudinal direction being determined so that upon the application of electromagnetic waves to said waveguide, no appreciable radiation exits from said elongated aperture in the reflecting member.

2. A waveguide structure comprising combination: a waveguide section having longitudinally extending conductive walls defining a waveguiding aperture adapted for the propagation of electromagnetic waves over a given range of radio frequencies in a longitudinal direction,

a radio frequency reflecting member closing off the said waveguide aperture of said waveguide section at one terminating end thereof, said member having an elongated aperture therein which beginning at the center line of the waveguide section extends toward the opposite conduc tive walls of the waveguide section, said member presenting at the border of said elongated aperture a pair of reflecting surfaces extending in said longitudinal direction, the width of said elongated aperture and the longitudinal length of said reflected surfaces being arranged so that upon the application of said waves to said waveguide section an effective short is provided by said reflecting member and no appreciable radiation occurs through said elongated aperture.

3. The combination claimed in claim 2 wherein said waveguide section is a rectangular waveguide having broad walls and narrow walls and said elongated aperture extends to the opposite broad walls.

4. An effectively closed-end waveguide structure comprising in combination:

a rectangular waveguide section adapted for operation over a given range of frequencies,

a pair of conductive plates closely spaced to each other at one end of said waveguide section so as to leave a narrow gap therebetween, said narrow gap being centered midway between the narrow walls of the waveguide, the spacing between said plates and thickness of said plates being arranged so that upon the application of signals over said given range of frequencies to said waveguide, no appreciable radiation exits from said waveguide at said end.

5. The combination claimed in claim 4 wherein said spacing between said plates is substantially less that one-half wavelength at the highest operating frequency of said waveguide and said thickness of said plates is at least about equal to said spacing.

6. A waveguide to microstrip transition structure comprising in combination:

a rectangular waveguide section adapted for operation over a given range of frequencies,

a pair of conductive end plates closely spaced to each other at one end of said waveguide section, the region between the plates being located midway between the narrow walls of said waveguide section, said region extending between the broad walls of said waveguide section,

said waveguide section having an elongated central aperture in each of the broad walls communicating with said region and extending from said one end into said waveguide section a distance approximately equal to one-quarter wavelength at a frequency within said given range of frequencies,

a ground planar conductor having an aperture adapted to receive therein said waveguide section, said waveguide section being positioned in said ground conductor aperture with said one end of said waveguide section approximately one-quarter wavelength from said ground cond uctor at a frequency within said given range of frequencies, said ground conductor being electrically connected to the walls of said waveguide section,

a dielectric slab having an elongated narrow strip-like con ductor on one surface thereof, said slab being fixed to said ground planar conductor to form a microstrip transmission line therewith, a portion of said dielectric slab and said narrow strip-like conductor extending through one of said elongated central apertures into said waveguide section in a manner to act as an electric field coupling device in said waveguide section. 

1. A waveguide structure comprising: a waveguide section having longitudinally extending conductive walls defining a waveguiding aperture adapted for the propagation of electromagnetic waves therealong over a given range of frequencies in a longitudinal direction, a reflecting member located at one terminating end of said waveguide section, said reflecting member having an elongated aperture and a pair of reflecting surfaces bordering opposite elongated sides of said elongated aperture, said elongated aperture being located so that an extension of the center line of said waveguide section passes through said elongated aperture and between said reflecting surfaces, the width of said elongated aperture and the length of said reflecting surfaces along the said longitudinal direction being determined so that upon the applIcation of electromagnetic waves to said waveguide, no appreciable radiation exits from said elongated aperture in the reflecting member.
 2. A waveguide structure, comprising in combination: a waveguide section having longitudinally extending conductive walls defining a waveguiding aperture adapted for the propagation of electromagnetic waves over a given range of radio frequencies in a longitudinal direction, a radio frequency reflecting member closing off the said waveguide aperture of said waveguide section at one terminating end thereof, said member having an elongated aperture therein which beginning at the center line of the waveguide section extends toward the opposite conductive walls of the waveguide section, said member presenting at the border of said elongated aperture a pair of reflecting surfaces extending in said longitudinal direction, the width of said elongated aperture and the longitudinal length of said reflected surfaces being arranged so that upon the application of said waves to said waveguide section an effective short is provided by said reflecting member and no appreciable radiation occurs through said elongated aperture.
 3. The combination claimed in claim 2 wherein said waveguide section is a rectangular waveguide having broad walls and narrow walls and said elongated aperture extends to the opposite broad walls.
 4. An effectively closed-end waveguide structure comprising in combination: a rectangular waveguide section adapted for operation over a given range of frequencies, a pair of conductive plates closely spaced to each other at one end of said waveguide section so as to leave a narrow gap therebetween, said narrow gap being centered midway between the narrow walls of the waveguide, the spacing between said plates and thickness of said plates being arranged so that upon the application of signals over said given range of frequencies to said waveguide, no appreciable radiation exits from said waveguide at said end.
 5. The combination claimed in claim 4 wherein said spacing between said plates is substantially less that one-half wavelength at the highest operating frequency of said waveguide and said thickness of said plates is at least about equal to said spacing.
 6. A waveguide to microstrip transition structure comprising in combination: a rectangular waveguide section adapted for operation over a given range of frequencies, a pair of conductive end plates closely spaced to each other at one end of said waveguide section, the region between the plates being located midway between the narrow walls of said waveguide section, said region extending between the broad walls of said waveguide section, said waveguide section having an elongated central aperture in each of the broad walls communicating with said region and extending from said one end into said waveguide section a distance approximately equal to one-quarter wavelength at a frequency within said given range of frequencies, a ground planar conductor having an aperture adapted to receive therein said waveguide section, said waveguide section being positioned in said ground conductor aperture with said one end of said waveguide section approximately one-quarter wavelength from said ground conductor at a frequency within said given range of frequencies, said ground conductor being electrically connected to the walls of said waveguide section, a dielectric slab having an elongated narrow strip-like conductor on one surface thereof, said slab being fixed to said ground planar conductor to form a microstrip transmission line therewith, a portion of said dielectric slab and said narrow strip-like conductor extending through one of said elongated central apertures into said waveguide section in a manner to act as an electric field coupling device in said waveguide section. 